PROJECT SUMMARY Lauretta A. Lacko, F32 Resubmission, 8/8/2018 Perinatal infections are a major cause of maternal and fetal illness, accounting for 2-3% of all congenital abnormalities. Zika virus (ZIKV) infection results in an increased risk of spontaneous abortion and poor intrauterine growth, although the mechanisms underlying fetal loss remain undetermined. Little is known about the impact of ZIKV infection during pre- and peri-implantation because most current studies in pregnancy models focus on post-implantation stages. The recent ZIKV epidemic is a growing public health concern as infection in pregnant woman not only causes abortion and poor growth, but also severe neurological consequences such as microcephaly. Notably, the most severe fetal abnormalities have been associated with infection during the first and second trimester of pregnancy. Given the rapid emergence of this devastating infectious disease, there is an urgent need to determine the in utero pathogenesis of ZIKV during early gestation. The overall objective of this study is to determine the effect of ZIKV infection at the earliest stages of pregnancy, or pre- and peri-implantation, on fetal and placental development, and to shed insight into possible mechanisms by which early infection increases risk of the disease. Recent studies have demonstrated ZIKV can infect first trimester immortalized trophoblast cell line and placental explants, but not mature human trophoblasts or explants isolated from late stage pregnancies. We hypothesize that trophectoderm cells (TECs) are a route for efficient mother to fetus viral transmission during early pregnancy, and can propagate the virus to further infect developing neural progenitor cells over time. Indeed, our preliminary studies (manuscript under peer review) demonstrate that ex vivo infection of murine blastocysts and human pre-implantation embryos results in efficient infection of TECs. Further, pre- and peri-implantation ZIKV infection can induce neural progenitor cell death at mid-gestation. In this proposal, we will define the cellular response of TECs to ZIKV infection in vivo (Aim 1) and dissect the molecular mechanism controlling ZIKV infection by studying the candidate genes identified from a CRISPR-based whole genome wide gene knockout screen (Aim 2). We will combine immunostaining, gene expression, and gene editing technologies to address these questions. These studies will provide fundamental insight into vertical transmission of ZIKV during the earliest stages of gestation. More importantly, it will shed a light into the mechanism regulating flavivirus and/or other viral infections during pregnancy.